Short Answer:

The start-up and shutdown procedure of thermal power plants is a systematic process that ensures safe and efficient operation of all plant components such as boilers, turbines, generators, and auxiliary systems. The start-up procedure involves gradually bringing the plant from a cold or standby condition to full operation, while the shutdown process carefully brings it back to rest to prevent damage.

In simple words, these procedures are step-by-step methods followed by operators to start or stop a thermal power plant safely. They maintain system stability, protect equipment from thermal stresses, and ensure smooth functioning without accidents or failures.

Detailed Explanation :

Start-up and Shutdown Procedure of Thermal Plants

The start-up and shutdown procedure of thermal power plants is a crucial operation that requires careful control and monitoring of all systems. Thermal power plants work on the Rankine cycle, where heat energy from fuel is converted into mechanical and then electrical energy through boilers, turbines, and generators. Since these components operate under high temperature and pressure, proper start-up and shutdown procedures are essential to prevent thermal stress, equipment damage, and safety hazards.

Start-up involves gradual heating and pressurization of the plant’s systems, while shutdown involves controlled cooling and depressurization. Both processes are carried out in stages and follow standard operational guidelines to ensure safety, reliability, and efficiency.

Start-up Procedure of Thermal Plants

The start-up procedure refers to the process of starting the plant from a cold, warm, or hot condition to reach its full load operation. The steps depend on the plant’s design and operational condition.

1. Pre-Start Checks:
   Before starting the plant, several inspections are carried out to ensure that all systems are in good condition.

• Check fuel, water, and air supply systems.
• Inspect boiler tubes, valves, and pumps for leakage.
• Ensure lubrication oil systems are functioning properly.
• Verify electrical systems, control panels, and instrumentation.
• Confirm that safety interlocks and alarms are active.

Once all checks are complete, operators prepare the systems for gradual heating.

2. Boiler Start-up:
   The boiler start-up is the first major step.

• Start feedwater pumps and ensure water level in the drum is within safe limits.
• Start the forced draft fan (FDF) to supply air for combustion.
• Open the air vents to remove air from the boiler circuit.
• Start the fuel system and ignite burners using auxiliary fuel (like oil or gas).
• Gradually increase the furnace temperature to allow uniform heating.
• Close vents when steam generation begins.
• Monitor steam pressure and temperature carefully to avoid thermal shocks.

The steam is slowly raised to the desired pressure and quality before supplying it to the turbine.

3. Turbine Start-up:
   After steam is generated, the turbine is started.

• Ensure lubricating oil system is running and oil pressure is adequate.
• Rotate the turbine shaft using a barring gear (turning gear) to prevent uneven heating.
• Admit small amounts of steam to warm the turbine casing evenly.
• Gradually increase steam pressure and speed up the turbine.
• Observe vibration, temperature, and bearing conditions.
• When the turbine reaches its rated speed, synchronize it with the generator.

Synchronization ensures that the generator output frequency and voltage match the grid conditions.

4. Generator Synchronization and Load Application:

• Match the generator voltage, frequency, and phase with the power grid.
• Close the circuit breaker to connect the generator to the grid.
• Gradually increase load on the generator while monitoring current, voltage, and vibration.
• Adjust fuel and air supply according to load demand.

After synchronization, the plant is considered fully operational.

5. Monitoring During Start-up:
   Throughout the start-up phase, continuous monitoring is required to ensure stable operation.

• Observe temperature rise rates to avoid thermal stress.
• Check boiler drum water level and steam quality.
• Monitor turbine vibrations and bearing temperatures.
• Inspect condenser vacuum and cooling water flow.
• Verify that all safety systems are functional.

Any abnormal readings must be addressed immediately to prevent damage.

Shutdown Procedure of Thermal Plants

The shutdown procedure involves bringing the plant safely from operating condition to rest. Shutdown can be planned (for maintenance) or emergency (due to faults or failures).

1. Load Reduction:

• Gradually reduce generator load while maintaining grid stability.
• Adjust fuel supply and air flow to decrease steam generation.
• Slowly reduce turbine speed and output.

Sudden load removal is avoided to prevent thermal stress and mechanical strain.

2. Generator Disconnection:

• Once load is reduced to minimum, the generator is disconnected from the grid.
• Open the generator circuit breaker.
• Allow the turbine to run freely without load for cooling and balancing.

3. Turbine Shutdown:

• Close the steam inlet valve to stop steam supply to the turbine.
• Continue lubrication oil circulation to cool bearings.
• Allow the turbine to coast down to a stop using barring gear to prevent warping.
• Monitor bearing temperatures and vibration until the turbine stops completely.

4. Boiler Shutdown:

• Stop the fuel supply and allow the fire to burn out completely.
• Keep the forced draft fan and induced draft fan running to remove flue gases.
• Open vents and drains to release remaining steam safely.
• Maintain water circulation until boiler temperature drops to safe limits.
• Inspect water levels, pressure gauges, and safety valves.

5. Post-Shutdown Checks:
   After the plant is completely shut down:

• Isolate fuel, air, and water systems using valves.
• Record all operational parameters for analysis.
• Clean filters, strainers, and burners.
• Inspect mechanical and electrical systems for wear or leakage.
• Perform maintenance as required before the next start-up.

6. Safety Considerations During Shutdown:

• Ensure gradual cooling to avoid thermal stress on boiler tubes and turbine casings.
• Never drain water or open manholes until the boiler is fully depressurized.
• Keep lubrication systems running until all rotating parts stop.
• Verify that all interlocks and alarms are functioning for the next start-up.

Following these precautions ensures safe and damage-free shutdown.

Importance of Proper Start-up and Shutdown Procedures:

• Protects Equipment: Prevents damage due to thermal or mechanical stress.
• Ensures Safety: Avoids accidents caused by improper operation.
• Improves Efficiency: Maintains smooth performance of the system.
• Reduces Maintenance Costs: Minimizes wear and extends equipment life.
• Ensures Operational Reliability: Guarantees consistent and reliable power supply.

Thus, proper procedures are vital for safe and economical plant operation.

Conclusion:

The start-up and shutdown procedures of thermal power plants are critical for safe, efficient, and reliable operation. Start-up involves gradual heating, pressurization, and synchronization of systems, while shutdown involves careful load reduction, depressurization, and cooling. Both processes must be performed in a controlled sequence to avoid damage, ensure safety, and maintain plant performance. Following these systematic steps ensures long equipment life and stable power generation in thermal power plants.